2026 ICD-10-CM Diagnosis Code A51.0Primary genital syphilis

ICD-10-CM Codes›A00–B99›A50-A64›A51

ICD-10-CM A51.0
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A51.0 is a billable ICD-10-CM diagnosis code for primary genital syphilis. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 727 through 728, 742 through 743, 757 through 759. Coders also document this condition as bacterial balanitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Sexually transmitted infections (excluding HIV and hepatitis).

Code Identity

ICD-10-CM Code
A51.0
Billable Status
Yes — Valid for Submission
Code Describes
Primary genital syphilis
Short Description
Primary genital syphilis
Same as the full description in the CMS dataset.
Parent Code
A51
Early syphilis

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA50-A64Infections with a predominantly sexual mode of transmission
CategoryA51Early syphilis
This CodeA51.0Primary genital syphilis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Bacterial balanitis
  • Infective dermatosis of female genitalia
  • Primary genital syphilis
  • Primary syphilis
  • Syphilitic balanitis
  • Syphilitic chancre
  • Syphilitic chancre of penis
  • Syphilitic chancre of vulva

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Syphilitic chancre NOS

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Bubo
      • syphilitic (primary)
    • Chancre(any genital site) (hard) (hunterian) (mixed) (primary) (seronegative) (seropositive) (syphilitic)
    • Chancre(any genital site) (hard) (hunterian) (mixed) (primary) (seronegative) (seropositive) (syphilitic)
      • urethra
    • Lesion(s) (nontraumatic)
      • primary
    • Syphilis, syphilitic(acquired)
      • bubo (primary)
    • Syphilis, syphilitic(acquired)
      • chancre (multiple)
    • Syphilis, syphilitic(acquired)
      • chancre (multiple)
        • Rollet's
    • Syphilis, syphilitic(acquired)
      • early
        • symptomatic
          • primary, except extragenital chancre
    • Syphilis, syphilitic(acquired)
      • genital (primary)
    • Syphilis, syphilitic(acquired)
      • penis (chancre)
    • Syphilis, syphilitic(acquired)
      • primary
    • Syphilis, syphilitic(acquired)
      • primary
        • genital
    • Syphilis, syphilitic(acquired)
      • vagina
    • Syphilis, syphilitic(acquired)
      • vulva
    • Ulcus
      • durum (syphilitic)
    • Vaginitis(acute) (circumscribed) (diffuse) (emphysematous) (nonvenereal) (ulcerative)
      • syphilitic (early)
    • Vulvitis(acute) (allergic) (atrophic) (hypertrophic) (intertriginous) (senile)
      • syphilitic (early)

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INF010
Sexually transmitted infections (excluding HIV and hepatitis)
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Primary Syphilis

    the subclinical or symptomatic stage of syphilis, occurring at an average of three weeks after contact with an infected individual. it manifests with one or more painless, indurated ulcers (chancres) of the skin or mucous membranes at the site of inoculation. these lesions heal spontaneously within a few weeks.

Patient EducationClinical

Syphilis

Syphilis is a sexually transmitted infection (STI) caused by bacteria. It infects the genital area, lips, mouth, or anus of both men and women. You usually get syphilis from sexual contact with someone who has it. It can also pass from mother to baby during pregnancy.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert A51.0 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
091.0 Primary genital syphilis
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About A51.0Overview

Is A51.0 (Early syphilis) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report primary genital syphilis on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does A51.0 group to?

When primary genital syphilis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 727, 728, 742, 743, 757, 758, 759, with relative weights from 0.6636 to 1.8348 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of A51.0?

Under the General Equivalence Mappings, primary genital syphilis converts to ICD-9-CM 091.0 (primary genital syphilis). The mapping is a direct match.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.